net: kcov: don't select SKB_EXTENSIONS when there is no NET

Fix kconfig warning when CONFIG_NET is not set/enabled:

WARNING: unmet direct dependencies detected for SKB_EXTENSIONS
  Depends on [n]: NET [=n]
  Selected by [y]:
  - KCOV [=y] && ARCH_HAS_KCOV [=y] && (CC_HAS_SANCOV_TRACE_PC [=y] || GCC_PLUGINS [=n])

Fixes: 6370cc3 ("net: add kcov handle to skb extensions")
Signed-off-by: Randy Dunlap <[email protected]>
Cc: Aleksandr Nogikh <[email protected]>
Cc: Willem de Bruijn <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: rddunlap

lib/Kconfig.debug

@@ -1870,7 +1870,7 @@ config KCOV
 	depends on CC_HAS_SANCOV_TRACE_PC || GCC_PLUGINS
 	select DEBUG_FS
 	select GCC_PLUGIN_SANCOV if !CC_HAS_SANCOV_TRACE_PC
-	select SKB_EXTENSIONS
+	select SKB_EXTENSIONS if NET
 	help
 	  KCOV exposes kernel code coverage information in a form suitable
 	  for coverage-guided fuzzing (randomized testing).